1. Field of the Invention
The present invention relates to the field of agriculture, and in particular to the mulching of agriculture soil beds using a thin protein film as a mulch layer. More particularly the invention relates to the mulching of agricultural crop growing plots by spreading a protein solution thereon and allowing the solution to dry to form a thin mulching film of protein lying over the plot.
2. Prior Activities and Problems in the Field
Mulch is defined as a protective covering used on the ground generally over a growing crop to reduce evaporation, prevent erosion, control weeds, and/or enrich the soil. There are many kinds of materials that may be used for mulching, for example, compost, sheet composting, humus, organic mulches, seed free mulches, green growing mulches, etc. Compost, humus and organic matter mulches are generally used in small gardens and fields having small cropping areas. Polyethylene mulch is a material most commonly used on farms at the present time to conserve soil moisture, prevent soil erosion, modify soil temperature, and control weeds, with resulting improvements in yield, quality, earliness of harvest, and efficiency of management.
An undesirable consequence of using a conventional polyethylene mulch, however, is that polyethylene does not readily decompose in nature. This creates additional operations for the producer to pick up the mulch and dispose of it. Unfortunately, it has been observed that non-biodegradable mulches, such as polyethylene film, are often disposed of by burning, by being pushed aside or by dumping in a landfill. These disposal methods either give off harmful fumes or create more waste in the environment.
During the last several decades, tremendous strides have been made to enhance the usefulness of artificial mulches. This is due to the development of new and improved materials and new and improved techniques and machinery with which to perform the necessary operations. Mulches consisting of styrene-butadiene polymer dispersions have been developed. Such mulches may be sprayed on soil and dried to a film. Moreover these mulches provide many of the desirable effects of a plastic mulch, and yet the material is biodegradable such that it can be plowed under following harvest. No mulch waste is produced that needs collecting and disposing of away from the field.
Development of biopolymer films and coatings from proteins, polysaccharides and lipid materials have received increased interest in recent years. In the midst of rising concerns over environmental protection, the renewable nature of biopolymer film ingredients renders such films particularly appealing for innovative uses in the field as mulch. Furthermore, since many of these film-forming biopolymers are edible, it is obvious that a biodegradable mulch may be readily prepared therefrom. Films prepared from proteins such as wheat gluten, corn zein, soy proteins, peanut proteins, milk proteins, collagen and gelatin have been developed and tested for selected physical and mechanical properties. Recent studies have concentrated on the development and property evaluation of films made from soy protein isolate and wheat gluten.
Ongoing research projects at the Industrial Agricultural Products Center (IAPC) of the University of Nebraska involve modification of biopolymers for incorporation into plastic films. Recent publications authored by researchers working at IAPC provide an up-to-date review of research on edible films and coatings produced from grain proteins. Both publications are extensive reviews and interested readers are referred to Gennadios, A, and C. L. Weller (1990) xe2x80x9cEdible Films and Coatings From Wheat and Corn Proteinsxe2x80x9d, Food Technology 44(10): 63-69; and Gennadios, A. and C. L. Weller (1991), xe2x80x9cEdible Films and Coatings From Soybeans and Soy Proteinxe2x80x9d, Cereal Foods World 36(12):1004-1009.
Comprehensive reviews on the film-forming properties of several protein, polysaccharide, and lipid substances have recently been published. (See Guilbert, S. (1986), xe2x80x9cTechnology and Application of Edible Protective Filmsxe2x80x9d, Food Packaging and Preservation: Theory and Practice, ed. M. Mathlouthi, 371-394, Elsevier Applied Science Publishers, Ltd. (London); Guilbert, S. (1988), xe2x80x9cUse of Superficial Edible Layer to Protect Intermediate Moisture Foods: Application to the Protection of Tropical Fruits Dehydrated by Osmosis, Food Preservation by Moisture Control, ed. C. C. Seow, 199--219, Elsevier Applied Science Publishers, Ltd. (London); Kester, J. J. and O. R. Fennema (1986), xe2x80x9cEdible Films and Coatings: A Reviewxe2x80x9d, Food Technology 40(12), 47-59; and Krochta, J. M. (1992), xe2x80x9cControl of Mass Transfer in Foods with Edible Coatings and Filmsxe2x80x9d, Advances in Food Engineering, ed. R. P. Singh and M. A. Wirakartakusumah, 517-538, CRC Press, Inc. (Boca Raton, Fla.)). Protein films in particular have also been discussed in detail by Gennadios and others (See A. Gennadios, T. H. McHugh, C. L. Weller and J. M. Krochta (1993), xe2x80x9cEdible Coatings and Films Based on Proteinsxe2x80x9d, Edible Coatings and Films to Improve Food Quality, ed. J. M. Krochta, M. Nisperos-Carriedo and E. A. Baldwin (In press), Technomic Publishing Company, Inc. (Lancaster, Pa.); A. Gennadios, A. H. Brandenburg, C. L. Weller and R. F. Testin, (1993), xe2x80x9cEffect of pH on Properties of Wheat Gluten and Soy Protein Isolate Filmsxe2x80x9d, Journal of Agricultural and Food Chemistry 41:1835 -1839; A. Gennadios, A. H. Brandenburg, A. H. Park, C. L. Weller and R. F. Testin (1993), xe2x80x9cWater Vapor Permeability of Wheat Gluten and Soy Protein Isolate Filmsxe2x80x9d, Industrial Crops Products (In press); A. Gennadios, H. J. Park and C. L. Weller (1993), xe2x80x9cRelative Humidity and Temperature Effects on Tensile Strength of Edible Protein and Cellulose Ether Filmsxe2x80x9d, Transactions of the ASAE (In press); A. Gennadios, C. L. Weller and R. F. Testin (1993), xe2x80x9cTemperature Effect on Oxygen Permeability of Edible Protein-Based Filmsxe2x80x9d, Journal of Food Science 58:212-214, 219; A. Gennadios, C. L. Weller and R. F. Testin (1993), xe2x80x9cModification of Properties of Edible Wheat Gluten-Based Filmsxe2x80x9d, Transactions of the ASAE 36: 465-470; A. Gennadios, C. L. Weller and R. F. Testin (1993), xe2x80x9cModification of Physical and Barrier Properties of Edible Wheat Gluten-Based Filmsxe2x80x9d, Cereal Chemistry 70:426-429; A. Gennadios, C. L. Weller and C. H. Gooding (1993), xe2x80x9cMeasurement errors in Water Vapor Permeability of Highly Permeable, Hydrophilic Edible Filmsxe2x80x9d, Journal of Food Engineering (In press); A. Gennadios, C. L. Weller, M. A. Hanna and G. W. Froning (1993), xe2x80x9cEdible Films from Egg White Proteinxe2x80x9d, ASAE Paper No. 93-6037, ASAE (St. Joseph, Mich.)). Current Industrial applications of protein films include sausage casings from collagen (Hood, L. L. (1987), xe2x80x9cCollagen in Sausage Casingsxe2x80x9d, Advances in Meat Research 4:109-129); protective coatings of corn zein, usually mixed with acetylated monoglycerides, for use on nutmeats, medicinal tablets, and candy (Reiners, R. A., J. S. Wall and G. E. Inglett (1973), xe2x80x9cCorn Proteins: Potential for their Industrial Usexe2x80x9d, Industrial Uses of Cereals, ed. Y. Pomeranz, 285-302, American Association of Cereal Chemists (St. Paul, Minn.); Andres, C. (1984), xe2x80x9cNatural Edible Coating Has Excellent Moisture and Grease Barrier Propertiesxe2x80x9d, Food Processing 45(13): 48-49); and gelatin pharmaceutical capsules (Rose, P. I. (1987), xe2x80x9cGelatinxe2x80x9d, Encyclopedia of polymer Science and Engineering, ed. H. F. Mark, N. M. Bikales, C. G., Overberger and G. Menges, Vol. 7: 488-513, John Wiley and Sons, Inc.(New York)).
Considerable work is ongoing by various researchers related to edible films and coatings. Examples of some of these workers and their interests include: Krochta at UC-Davis-milk protein films (Ho, B. P., R. Avena-Bustillos and J. M. Krochta (1991), xe2x80x9cWater Vapor Permeability of CaseIn-Based Edible Filmsxe2x80x9d, Presented at AIChE Conference of Food Engineering (Chicago, Ill.); Fennema at Wisconsinxe2x80x94multi component films from cellulose and lipids (Greener, I. K. and O. Fennema (1989), xe2x80x9cBarrier Properties and Surface Characteristics of Edible Bilayer Filmsxe2x80x9d, J Food Sci. 54(6): 1393-1399); Labuza at Minnesotaxe2x80x94various film types (Koelsch, C. M. and T. P. Labuza (1991), xe2x80x9cStructural, Thermal and Functional Properties of Edible Fatty Acid Based Filmsxe2x80x9d, Presented at IFT Annual Meeting (Dallas, Tex.); Guilbert at the Centre d""Etudes et d""Expxc3xa9rimentation en Mxc3xa9canisation Agricole et Technologie alimentaire in France (Gontard, N., S. Guilbert and J-L. Cuq (1993), xe2x80x9cWater and Glycerol as Plasticizer Affect Mechanical and Water Vapor Barrier Properties of an Edible Wheat Gluten Filmxe2x80x9d, Journal of Food Science 58: 206-211); Torres at Oregon Statexe2x80x94cellulosic and lipid films (Anonymous (1991), xe2x80x9cNo More Soggy Ice Cream Conesxe2x80x9d, Dairy Herd Management 2:13.); Nisperos-Carriedo and associates at the USDA-ARS Citrus and Subtropical Products Research Labxe2x80x94cellulosic, shellac, and lipid films and coatings (Sanchez, D (1990), xe2x80x9cKeep in Under an Edible Coatxe2x80x9d, Agricultural Research 38(3):4-5; Hagenmaier, R. D. and P. E. Shaw (1990), xe2x80x9cMoisture Permeability of Edible Films Made with Fatty Acid and (Hydroxypropyl) Methylcellulose, J. Agric. Food Chern. 38:1799-1803); Wong, et al, at the USDA-ARS Western Regional Labxe2x80x94chitin coatings (Webb, T. (1991), xe2x80x9cEnd is in Sight for the Soggy Jelly Sandwichxe2x80x9d, Anderson Independent-Mall (Anderson, S. C.)); Narayan at the Michigan Biotechnology Institutexe2x80x94corn zein on paper (Rice, J. (1991), xe2x80x9cBiogradable Plasticsxe2x80x94Do They Have A Viable Future for Food Packaging Applications?xe2x80x9d, Food Processing 52(11):34-35,38,40); Chinnan at Georgiaxe2x80x94cellulosic and corn protein films and coatings (Park, H. J. and M. S. Chinnan (1990), xe2x80x9cProperties of Edible Coatings for Fruits and Vegetablesxe2x80x9d, ASAE Paper No. 90-6510, ASAE (St. Joseph, Mich.)); Herald at Kansas Statexe2x80x94wheat gluten films (Personal communication), and Baianu at Illinoisxe2x80x94various film types (Ozu, E. M., H. Y. Kim and I. C. Baianu(1991), xe2x80x9cDevelopment of Edible Films from Polysaccharides, Starch and Corn Proteinsxe2x80x9d, Presented at IFT Annual Meeting (Dallas, Tex.)).
Workers at IAPC have developed procedures to allow for the production of homogeneous corn, wheat and soy protein films. Several different formulations for use in formation of wheat gluten films have been studied. The formulations differ in the type and amount of plasticizer added to the film mixture. Efforts in enhancement include soaking the films in buffer, salt, or tanning solutions; or supplementing the film formula with other substances such as keratin and/or surfactants. Evaluation of the barrier and mechanical properties of these latest films show that incorporation of additives, modification of film-forming solutions, and soaking treatments all improve the films to some extent. However, an order of magnitude improvement is desirable for increasing the commercial exploitability of the films. Further improvement of film properties, especially to increase moisture barrier ability, presents a challenge. Tailoring of protein films to specific applications often requires a thorough evaluation of the properties of the film. Several studies have reported property characteristics of protein films from wheat gluten, corn zein, soy protein, caseiso and egg albunin. (In addition to the references cited above, also see T. P. Aydt, C. L. Weller, and R. F. Testin (1991), xe2x80x9cMechanical and Barrier Properties of Edible Corn and Wheat Protein Filmsxe2x80x9d, Transactions of the ASAE 34(1):207-211; N. Gontard, S. Guilbert and J-L. Cuq (1992), xe2x80x9cEdible Wheat Gluten Films: Influence of the Main Process Variables on Film Properties Using Response Surface Methodologyxe2x80x9d, Journal of Food Science 57: 190-195, 199; A. H. Brandenburg, C. L. Weller and R. F. Testin (1993), xe2x80x9cEdible Films and Coatings From Soy Proteinxe2x80x9d Journal of Food Science 58:1086-1089; and T. H. McHugh, R. Avena-Bustillos and J. M. Krochta (1993), xe2x80x9cHydrophillo Edible Films: Modified Procedure for Water Vapor Permeability and Explanation of Thickness Effectsxe2x80x9d, Journal of Food Science 58:899-903).
Efforts to improve water barrier properties begin with the understanding that films of proteinaceous material may be formed due to the presence of side groups on many amino acids. These groups function easily to form hydrogen bonds, ionic bonds and even covalent bonds between molecular chains. There are many reactive sites available on protein polymeric chains, and wheat protein will form crosslinks by hydrophobic interactions due to the large number of hydrophobic amino acid sites. Efforts to decrease the hydrophillic nature of wheat protein films have focussed on two important insolubilization mechanisms. The first mechanism involves a reaction with hydrophilic groups on the protein polymers to block them thereby causing them to have a reduced affinity for water. The second mechanism involves a crosslinking reaction between adjacent molecules to thereby form a reinforced structure rigid enough to resist swelling when wetted. Resinous material, such as polyethylene, is most effective for this purpose. Groups on protein polymers, such asxe2x80x94NH2,xe2x80x94SH,xe2x80x94OH,xe2x80x94COOH andxe2x95x90NH, may contribute to the crosslinking reaction through the use of various catalytic and other agents. These functional groups on the amino acids can be crosslinked or grafted onto polyethylene. The side chains of threonine and serine specifically may be attached chemically to remove H2O molecules and create a xe2x80x94Cxe2x95x90Cxe2x80x94group which is quite active in graft copolymerization with polyethylene.
Grafting acrylates and vinyl chain polymers onto proteins using the ceric ion method has been well documented. Ceric ion forms an effective redox system in the presence of organic reducing agents such as alcohols, glycols, aldehydes, acetals, thiols, esters and carboxylic acids. Ceric ammonium nitrate has been used as an initiator by Rao and co-workers (K. P. Rao, K. T. Joseph, and Y. Nayudamma (1972), xe2x80x9cCharacterization of the Collagen-Vinyl Graft Copolymers Prepared by the Ceric Ion Methodxe2x80x9d, II Infrared spectra and electron microscopy 16: 975-986) to graft methyl methacrylate acrylonitrile and acrylamide to collagen. Mino and Kaizeman (G. Mino and S. Kalzerman (1958), J. Polym. Sci. 31:242) showed that alcohols form a ceric ion alcohol complex and that the dissociation of this complex is a rate limiting step. Since wheat gluten contains alcoholic groups and several amino acids, grafting monomers can be successfully performed by the ceric ion method. Graft polymerization reactions may also be carried out with other active groups of wheat gluten.
Plastic mulches have been used for several decades, but very limited research has been reported on the use of environmentally friendly biodegradable materials as mulches. Brown et al. (1992), in the department of Horticulture at Auburn University, used a blue-black styrofan at a rate of 959 L/ha in a pepper field and reported that yields were similar for the styrofan and plastic mulch treatments. These investigators suggested that styrofan could be used as an alternative for conventional black polyethylene mulch. The cost of styrofan application is high. However, savings on investment and labor costs could result because styrofan is biodegradable and does not require additional equipment and labor for removal from field.
It is a primary objective of the present invention to provide a method for mulching an agricultural soil bed using a thin protein film. In accordance with the method a film forming solution of a film forming protein material is prepared. A quantity of the protein solution is then spread directly over a surface of an agricultural soil bed. The quantity preferably is sufficient to provide a thin mulching film of the protein material on the surface of the agricultural soil bed after the solution has dried. The protein solution on the surface may then be allowed to dry to thereby form a thin film of protein material on the surface.
In one preferred form of the invention, the film forming protein solution may comprise an aqueous solution of soy protein isolate. In a particularly preferred form of the invention the protein solution may be alkaline and may comprise from about 2 to about 10% by weight glycerine and from about 5 to about 15% by weight of the protein isolate.
In another preferred form of the invention, the film forming protein solution may comprise an aqueous solution of wheat gluten. In a particularly preferred form of this aspect of the invention, the solution may be alkaline and may comprise from about 2 to about 10% by weight glycerine, from about 35 to about 70% by weight ethanol, from about 35 to about 70% by weight water and from about 2 to about 15% by weight of the wheat gluten.
In accordance with the invention, the protein material used to form the thin film of protein material may comprise one or more of a plant protein, a milk protein, an animal protein, a whey protein, casein, an egg protein and a gelatin.
Generally speaking the film forming solution may be an alkaline aqueous solution, a soy bean protein isolate solution may comprise from about 8 to about 12 weight % solids and a wheat gluten solution may comprise from about 4 to about 6 weight % solids.
A sufficient amount of the soy bean protein isolate solution may be spread uniformly over the surface of an agricultural soil bed to provide a film of soy bean protein isolate material weighing from about 175 to about 225 pounds per acre on the surface of the plot after the solution has dried. Similarly, a sufficient amount of the wheat gluten protein solution may be spread over the surface of the agricultural plot to provide a film of wheat gluten protein material weighing from about 75 to about 125 pounds per acre on the surface of the plot after the solution has dried.
In accordance with another form of the invention, a method for producing an agricultural crop product is provided. This method comprises planting a potential agricultural product in a soil bed, spreading a quantity of a film forming solution of a film forming protein material directly over a surface of the planted soil bed, and allowing the protein solution on the surface to dry whereby to form a thin mulching film of protein material on the surface. Suffice it to say that in accordance with this form of the invention, the quantity of film forming solution spread on the surface of the planted soil bed should be sufficient to provide a thin mulching film of the protein material on the surface after the solution has dried.
In another form of the invention, an agricultural crop growing plot is provided. The agricultural crop growing plot may comprise a bed of soil and a planted potential agricultural product in the soil bed. In accordance with the invention, the agricultural crop growing plot also includes a thin film of protein material mulch on a surface of the soil bed over the product. The film may be formed by spreading a quantity of a film forming solution of a film forming protein material directly over the surface of the planted soil bed and allowing the protein solution on the surface to dry.